Internal mixing spray gun

ABSTRACT

A system, in certain embodiments, includes a spray device including a first liquid passage configured to flow a first liquid in a generally downstream direction toward a spray tip. The spray device also includes a second liquid passage configured to flow a second liquid in a generally upstream direction such that the second liquid impinges upon the first liquid at an outlet to the second liquid passage. The upstream direction is substantially opposite from the downstream direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/675,504, entitled “INTERNAL MIXING SPRAY GUN”, filed Nov. 13, 2012,which is a continuation of U.S. patent application Ser. No. 12/502,527,entitled “INTERNAL MIXING SPRAY GUN”, filed Jul. 14, 2009, now U.S. Pat.No. 8,322,632. Each of the foregoing applications is hereby incorporatedby reference in its entirety.

BACKGROUND

The invention relates generally to an internal mixing spray gun and,more specifically, to a system for effectively mixing multiple materialshaving substantially different viscosities and flow rates.

In many applications, two or more base materials are mixed together toachieve a material composition. The base materials may include differentliquids, solids, or some combination thereof. The characteristics of thematerial composition may depend significantly on the uniformity ofmixing of the two or more base materials. For example, if a resin and acatalyst are not adequately mixed together, then the materialcomposition may be weak due to uncured portions of the resin.Unfortunately, existing systems often fail to adequately mix such basematerials together, thereby reducing the quality of the final product.

BRIEF DESCRIPTION

A system, in certain embodiments, includes a spray device including afirst liquid passage configured to flow a first liquid in a generallydownstream direction toward a spray tip. The spray device also includesa second liquid passage configured to flow a second liquid in agenerally upstream direction such that the second liquid impinges uponthe first liquid at an outlet to the second liquid passage. The upstreamdirection is substantially opposite from the downstream direction.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagram illustrating an exemplary spray coating system inaccordance with certain embodiments of the present technique;

FIG. 2 is a flow chart illustrating an exemplary spray coating processin accordance with certain embodiments of the present technique;

FIG. 3 is a right side view of an exemplary spray coating device inaccordance with certain embodiments of the present technique;

FIG. 4 is a left side view of the spray coating device, as shown in FIG.3, in accordance with certain embodiments of the present technique;

FIG. 5 is a cross-sectional bottom view of the spray coating device,taken along line 5-5 of FIG. 4, in accordance with certain embodimentsof the present technique;

FIG. 6 is a perspective view of a valve body, as shown in FIG. 5, inaccordance with certain embodiments of the present technique;

FIG. 7 is a front view of the valve body, as shown in FIG. 5, inaccordance with certain embodiments of the present technique;

FIG. 8 is a cross-sectional side view of the valve body, taken alongline 8-8 of FIG. 7, in accordance with certain embodiments of thepresent technique;

FIG. 9 is a perspective view of a mixing baffle, as shown in FIG. 5, inaccordance with certain embodiments of the present technique;

FIG. 10 is a cross-sectional bottom view of the mixing baffle, takenalong line 10-10 of FIG. 9, in accordance with certain embodiments ofthe present technique;

FIG. 11 is a perspective view of an alternative embodiment of the valvebody shown in FIG. 6 in accordance with certain embodiments of thepresent technique; and

FIG. 12 is a cross-sectional front view of the spray coating device,taken along line 12-12 of FIG. 4, in accordance with certain embodimentsof the present technique.

DETAILED DESCRIPTION

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements. Anyexamples of operating parameters and/or environmental conditions are notexclusive of other parameters/conditions of the disclosed embodiments.

Spray guns configured to mix plural components may be employed to applya wide variety of materials, such as multi-component paints, urethanefoam, epoxy resin, and polyester or vinylester resin. For example,polyester or vinylester resin is typically utilized in the manufactureof fiberglass reinforced plastic (FRP) parts, such as boat hulls,bathtubs and shower stalls. The process of producing an FRP partgenerally includes applying sheets of fiberglass (e.g., chopped strandmat, woven roving, etc.) to a mold, and then spraying a combination of aresin and a catalyst onto the fiberglass. Once the resin and catalystare mixed, the resin beings to set, ultimately forming the plasticelement of the FRP composite structure.

As discussed below, the disclosed spray guns are configured tointernally mix multiple materials, such as the resin and catalyst, priorto spraying. The disclosed embodiments are configured to providesignificant internal mixing to produce a substantially homogeneousmixture, even with different materials (e.g., resin and catalyst) havingsignificantly different viscosities and flows rates. For example, anexample of a catalyst for polyester resins includes Methyl Ethyl KetonePeroxide (MEKP). The viscosity of MEKP may be approximately 10 timeslower than the viscosity of the resin. Furthermore, only 1% to 3% ofMEKP by volume may be utilized to catalyze polyester resins. Despite thesignificant differences in viscosity and flow rate, the disclosedembodiments of spray guns are configured to provide significant internalmixing in a compact space (e.g., short length) of the spray guns, ratherthan requiring long mixing sections. Thus, the disclosed spray guns maybe compact, easily maneuverable, and highly efficient at mixing multiplematerials. As a result, the disclosed spray guns reduce waste andincrease quality of the mixture applied to a target object, e.g.,increased strength of the FRP part.

Embodiments of the present disclosure may facilitate effective mixing ofmultiple materials having substantially different flow rates andviscosities within a spray gun. In certain embodiments, a spray gunincludes a first liquid passage configured to flow a first liquid in agenerally downstream direction toward a spray tip. The spray gun alsoincludes a second liquid passage extending within the first liquidpassage and configured to flow a second liquid in a generally upstreamdirection, substantially opposite from the downstream direction, suchthat the second liquid impinges upon the first liquid at an outlet tothe second liquid passage. The impingement of the second liquid upon thefirst liquid establishes a region of turbulent flow that serves to mixthe first liquid with the second liquid. Further embodiments includemultiple mixing baffles positioned downstream from the outlet to thesecond liquid passage. In such embodiments, each mixing baffle includesat least one set of converging passages configured to direct liquidflows toward one another. As one liquid flow impinges another, aturbulent flow is established that serves to further mix the firstliquid and the second liquid. In certain configurations, the at leastone set of converging passages of a first mixing baffle iscircumferential offset from the at least one set of converging passagesof another mixing baffle. This circumferential offset forces the liquidflow to follow a tortuous path through the baffles, thereby furthermixing the first and second liquids. The combination of these featuresmay result in effective mixing of the first liquid and the second liquiddespite significant differences in flow rate and viscosity.

FIG. 1 is a flow chart illustrating an exemplary spray coating system10, which comprises a spray coating device 12 for applying a desiredcoating to a target object 14. The spray coating device 12 may becoupled to a variety of supply and control systems, such as a liquidsupply 16, an air supply 18, and a control system 20. The control system20 facilitates control of the liquid and air supplies 16 and 18 andensures that the spray coating device 12 provides an acceptable qualityspray coating on the target object 14. For example, the control system20 may include an automation system 22, a positioning system 24, aliquid supply controller 26, an air supply controller 28, a computersystem 30, and a user interface 32. The control system 20 also may becoupled to a positioning system 34, which facilitates movement of thetarget object 14 relative to the spray coating device 12. Accordingly,the spray coating system 10 may provide a computer-controlled mixture ofcoating liquid, liquid and air flow rates, and spray pattern. Moreover,the positioning system 34 may include a robotic arm controlled by thecontrol system 20, such that the spray coating device 12 covers theentire surface of the target object 14 in a uniform and efficientmanner.

The spray coating system 10 of FIG. 1 is applicable to a wide variety ofapplications, liquids, target objects, and types/configurations of thespray coating device 12. In the present embodiment, the spray coatingdevice 12 is configured to internally mix multiple liquids prior tospraying. In such an embodiment, a user may select a first desiredliquid 40 from a plurality of different first coating liquids 42, and asecond desired liquid 44 from a plurality of different second coatingliquids 44. For example, the first coating liquid may be a resin and thesecond coating liquid may be a catalyst configured to cure the resin. Insuch a configuration, the first coating liquid may include polyester,vinylester, or epoxy resin, and the second coating liquid may includeMethyl Ethyl Ketone Peroxide (MEKP) or an Aliphatic Amine adduct, forexample. Certain embodiments may include unique features configured tofacilitate effective mixing of the first desired liquid 40 and thesecond desired liquid 44 despite significant differences in flow rateand viscosity. The user also may select a desired object 36 from avariety of different objects 38, such as different material and producttypes. For example, the target object may include fiberglass sheetsdisposed within a mold such that spraying a combination of resin andcatalyst onto the target forms a fiberglass reinforced plastic (FRP)part after the resin has cured. As discussed in further detail below,the spray coating device 12 also may comprise a variety of differentcomponents and spray formation mechanisms to accommodate the targetobject 14 and liquid supply 16 selected by the user. For example, thespray coating device 12 may comprise an air atomizer, a rotary atomizer,an electrostatic atomizer, or any other suitable spray formationmechanism.

FIG. 2 is a flow chart of an exemplary spray coating process 100 forapplying a desired spray coating to the target object 14. Asillustrated, the process 100 proceeds by identifying the target object14 for application of the desired liquids, as represented by block 102.The process 100 then proceeds by selecting the desired liquids forapplication to a spray surface of the target object 14. Specifically, auser selects a first liquid 40, as represented by block 104, and thenselects a second liquid 44, as represented by block 105. As will beappreciated, the second liquid 44 may be selected based on the selectionof the first liquid 40. For example, if the first desired liquid 40 is aresin, the second desired liquid 44 may be a catalyst configured toeffectively cure the selected resin. As discussed in detail below,certain embodiments may include unique features configured to facilitateeffective mixing of the first desired liquid 40 and the second desiredliquid 44 despite significant differences in flow rate and viscosity. Auser may then proceed to configure the spray coating device 12 for theidentified target object 14 and selected liquids, as represented byblock 106. As the user engages the spray coating device 12, the process100 then proceeds to create a spray of the selected liquids, asrepresented by block 108. The user may then apply a coating of the sprayover the desired surface of the target object 14, as represented byblock 110. Next, as represented by block 112, the process 100 proceedsto cure/dry the coating applied over the desired surface. If anadditional coating of the selected liquids is desired by the user atquery block 114, then the process 100 proceeds through blocks 108, 110,and 112 to provide another coating of the selected liquids. If the userdoes not desire an additional coating of the selected liquids at queryblock 114, then the process 100 proceeds to query block 116 to determinewhether a coating of new liquids is desired by the user. If the userdesires a coating of new liquids at query block 116, then the process100 proceeds through blocks 104-114 using new selected liquids for thespray coating. If the user does not desire a coating of new liquids atquery block 116, then the process 100 is finished at block 118.

FIG. 3 is a right side view of an exemplary embodiment of the spraycoating device 12. As illustrated, the spray coating device 12 includesa body 202 configured to receive and mix multiple liquids prior tospraying. The spray coating device 12 also includes a nozzle assembly204. As discussed in detail below, the nozzle assembly 204 includes astatic mixer configured to provide additional mixing of the liquids. Thenozzle assembly 204 also includes a discharge orifice or spray tip 205that ultimately directs the liquids toward the target 14. Theillustrated spray tip 205 includes two converging exit orificesconfigured to direct streams of liquid toward one another. This type ofspray tip 205 may be described as an impingement tip, and provides arelatively coarse spray pattern. Such a spray pattern may be well suitedfor applications involving spraying resin and catalyst to form FRPparts. Alternative embodiments may include different spray tips 205,such as atomizer tips for applying gel coats, or the like. Furthermore,the nozzle assembly 204 of the present embodiment is configured to beremovable from the body 202 such that a particular nozzle assembly 204may be selected for a specific application.

The spray coating device 12 also includes connectors and conduitsconfigured to deliver a first liquid and a second liquid into the body202. Specifically, FIG. 3 shows the second liquid conduit 206 and thesecond liquid inlet 208. In the present configuration, the second liquidmay be a catalyst configured to cure a resin (i.e., first liquid). Forexample, in certain embodiments, the first liquid is a polyester resinand the second liquid is MEKP. In such configurations, the second liquidconduit 206 may be configured to flow approximately 1% to 3% of thevolume of the first liquid conduit, thereby establishing a volumetricratio of resin and catalyst within a mixing portion of the body 202 toachieve proper curing.

The spray coating device 12 further includes a trigger 210 configured toregulate the flow of the first and second liquids into the body 202.Specifically, the trigger 210 is rotationally coupled to the body 202 ata pivot point 212. The trigger 210 is also coupled to needle valves thatcontrol the flow of the first and second liquids. As illustrated, thetrigger 210 includes a mount 214. A shaft 216 coupled to the secondliquid needle valve (i.e., 301 of FIG. 5) extends through an openingwithin the mount 214. A fastener 218 is secured to an opposite end ofthe shaft 216 from the needle valve. As the trigger 210 is rotated in adirection 211 about the pivot point 212, the mount 214 contacts thefastener 218. Further rotation of the trigger 210 moves the shaft 216 ina direction 213 via contact between the mount 214 and the fastener 218.Movement of the shaft 216 opens the second liquid needle valve andinitiates flow of the second liquid into a mixing portion of the body202. As discussed in detail below, the mixing portion includes anassembly configured to flow the second liquid in a substantiallyupstream direction 221 relative to the downstream flow 219 of the firstliquid. Impingement of the second liquid upon the first liquid mayestablish a turbulent flow that enhances mixing of the two liquids.Furthermore, mixing baffles employing circumferentially offsetconverging passages may be positioned downstream from the outlet of thesecond liquid to further facilitate mixing. The combination of thesefeatures may result in effective mixing of the first liquid and thesecond liquid despite significant differences in flow rate andviscosity.

FIG. 4 is a left side view of the spray coating device 12 shown in FIG.3. As illustrated, a first liquid conduit 220 including a first liquidinlet 222 extends into the body 202. As previously discussed, the firstliquid conduit 220 is configured to flow a significantly higher volumeof liquid into the body 202 than the second liquid conduit 206. Similarto the arrangement described above with regard to the second liquid, thetrigger 210 is configured to regulate the flow of first liquid into thespray coating device 12. Specifically, a shaft 224 is disposed throughthe trigger 210 and coupled to a fastener 226. As the trigger 210rotates in the direction 211 about the pivot point 212, contact betweenthe trigger 210 and the fastener 226 causes the shaft 224 to move in thedirection 213 away from the body 202. Because the shaft 224 is coupledto a needle valve (i.e., 329 of FIG. 5) within the body 202, movement ofthe shaft 224 in the direction 213 causes the needle valve to open,thereby facilitating a flow of first liquid into the mixing portion ofthe body 202.

FIG. 4 also illustrates a liquid flushing system 228 configured to flowa solvent through the spray coating device 12. Because the spray coatingdevice 12 is configured to receive and mix a resin and a catalyst, anyliquid remaining in the body 202 after use may begin to set andeventually cure. Therefore, the liquid flushing system 228 is configuredto flow a solvent through the mixing portion of the body 202 afterspraying of the liquids is complete to substantially remove the liquidsfrom the spray coating device 12. Specifically, the liquid flushingsystem 228 includes an inlet 230 and an activation switch 232. Asdiscussed in detail below, depression of the activation switch 232engages a flow of solvent through the inlet 230 into the body 202. Thesolvent is configured to dissolve and remove residual liquids from thespray coating device 12 to substantially reduce or eliminate thepossibility that resin may cure within the body 202 and interfere withoperation of the spray coating device 12.

FIG. 5 is a cross-sectional bottom view of the spray coating device 12,taken along line 5-5 of FIG. 4. As previously discussed, the shaft 216is coupled to a needle valve 301 configured to regulate the flow ofsecond liquid into the mixing portion of the body 202. Specifically, theshaft 216 is coupled to a compression spring 302 configured to bias theneedle valve 301 into a closed position. A secondary shaft 304 extendsbetween the shaft 216 and a plunger 306. While in the closed position,the plunger 306 blocks the flow of second liquid from an inlet 308,which is coupled to the second liquid conduit 206. Specifically, theplunger 306 is disposed within an orifice 310 contoured to correspond tothe shape of the plunger 306, thereby forming a seal when the needlevalve 301 is in the closed position. As the trigger 210 rotates aboutthe pivot 212, contact between the mount 214 and the fastener 218 causesthe shaft 216 to move away from the body 202 and compress the spring302. As the spring 302 compresses, coupling between the shaft 216 andthe secondary shaft 304 causes the plunger 306 to exit the orifice 310,thereby facilitating liquid flow from the inlet 308 through orifice 310.

The second liquid then flows through a conduit 312 to a mixing portion313 of the body 202. The second liquid first enters an annular recess orcavity 314 disposed within the mixing portion 313. The annular cavity314 serves to distribute the second liquid substantially evenly aboutthe circumference of a valve body 315. The second liquid then enters thevalve body 315 via conduits 316 extending radially through the valvebody 315 between the cavity 314 and a central chamber 318. A check valve319 is disposed adjacent to the central chamber 318 and serves to blockthe flow of first liquid into the central chamber 318. As illustrated,the check valve 319 includes a shaft 320, a retainer 322, and acompression spring 324, each being disposed within a central opening orcavity 326. The second liquid flows from the central chamber 318 througha gap between the retainer 322 and the central cavity 326, and thenthrough a space between the shaft 320 and the central cavity 326 (i.e.,adjacent to the compression spring 324). While in a closed position, thecheck valve 319 blocks the flow of the second liquid. Specifically, ahead 327 of the shaft 320 is biased against the valve body 315 by thecompression spring 324, thereby restricting the flow of second liquid.

As discussed in detail below, a mixing chamber 328 is disposed adjacentto the head 327 and contains the first liquid. The check valve 319 isconfigured to open when the liquid pressure of the second liquid isgreater than the liquid pressure of the first liquid plus an additionpressure sufficient to overcome the spring bias of the check valve 319.For example, in certain configurations, the liquid pressure of thesecond liquid is approximately 300 psi and the liquid pressure of thefirst liquid is approximately 200 psi. In such configurations, thepressure sufficient to overcome the spring bias may be less than 100psi. Therefore, when the second liquid enters the central cavity 326,the liquid pressure may be sufficient to open the check valve 319 andfacilitate mixing of the second liquid with the first liquid in themixing chamber 328. Furthermore, because the pressure of the secondliquid is greater than the pressure of the first liquid, the mixturewill not flow back through the check valve 319. If the pressure of thesecond liquid drops below the pressure of the first liquid (plus thepressure sufficient to overcome the spring bias), the check valve willclose, thereby blocking the flow of the first liquid into the centralcavity 326. This configuration substantially reduces or eliminates thepossibility of liquid mixing within the flow path of the second liquid.

Similar to the arrangement described above with respect to the secondliquid flow path, flow of the first liquid is regulated by a needlevalve 329. Specifically, the shaft 224 is coupled to a compressionspring 330 configured to bias the needle valve 329 into a closedposition. A secondary shaft 332 extends between the shaft 224 and aplunger 334. While in the closed position, the plunger 334 blocks theflow of first liquid from an inlet 336, which is coupled to the firstliquid conduit 220. As illustrated, the plunger 334 is disposed withinan orifice 338 contoured to correspond to the shape of the plunger 334,thereby forming a seal when the needle valve 329 is in the closedposition. As the trigger 210 rotates about the pivot 212, contactbetween the trigger 210 and the fastener 226 causes the shaft 224 tocompress the spring 330. As the spring 330 compresses, coupling betweenthe shaft 224 and the secondary shaft 332 causes the plunger 334 to exitthe orifice 338, thereby facilitating liquid flow from the inlet 336through orifice 338.

With the needle valve 329 in the open position, the first liquid flowsin a generally downstream direction 219 from the orifice 338 to thenozzle assembly 204. Specifically, the first liquid flows from theorifice 338 into the mixing chamber 328. As previously discussed, thesecond liquid flows into the mixing chamber 328 in a generally upstreamdirection 221, substantially opposite from the downstream direction 219(e.g., approximately 180 degrees relative to one another). In thepresent embodiment, the second liquid enters the mixing chamber 328through a substantially annular orifice formed by the gap between thehead 327 of the check valve shaft 320 and the valve body 315. Theannular orifice is configured to provide a generally even distributionof second liquid into the first liquid present in the mixing chamber328. Because the first liquid is flowing in a generally downstreamdirection 219 and the second liquid is flowing in a generally upstreamdirection 221, interaction between the liquids induces a turbulent flowwithin the mixing chamber 328, thereby effectively mixing the firstliquid with the second liquid.

As previously discussed, the liquid pressure of the second liquidexiting the check valve 319 is greater than the pressure of the firstliquid within the mixing chamber 328. Therefore, flow of the mixedliquid is blocked from entering the central opening 326. As a result,the liquid mixture is directed in a generally downstream direction 219into the mixing portion 313 of the body, i.e., between the valve body315 and an inner surface of the mixing portion 313. The liquid thenpasses through a first mixing baffle 340. As discussed in detail below,the first mixing baffle 340 includes multiple sets of convergingpassages, each set configured to direct liquid flows toward one another.As one liquid flow impinges another, a turbulent flow is establishedthat serves to further mix the first liquid and the second liquid. Theliquid mixture then flows through a second mixing baffle 342 similar tothe first mixing baffle 340 to further mix the liquids. In certainconfigurations, the converging passages of the first baffle 340 arecircumferential offset (i.e., shifted along a circumferential direction347) from the converging passages of the second baffle 342. Thiscircumferential offset forces the liquid flow to follow a tortuous paththrough the baffles 340 and 342, thereby further mixing the first andsecond liquids.

After passing through the baffles 340 and 342, the mixed liquidcontinues to flow in the downstream direction 219. Specifically, theliquid passes through flow passages within a downstream section 344 ofthe valve body 315. The flow then passes through a passage 346downstream of the valve body 315 and enters a static mixer 348 withinthe nozzle assembly 204. The static mixer 348 includes a series ofturning vanes, each configured to split the flow in half and rotate eachhalf approximately 90 degrees. The splitting and turning motion servesto further mix the liquid. The present configuration includes fourturning vanes. However, alternative configurations may employ more orfewer vanes. For example, certain configurations may include 0, 1, 2, 3,4, 5, 6, 7, 8, or more vanes in the static mixer 348. After passingthrough the static mixer 348, the liquid exits the spray tip 205. Themixing features within the spray coating device 12 serve to effectivelymix the first liquid with the second liquid despite significantdifferences in flow rate and viscosity. Furthermore, the combination ofimpinging flow and the mixing baffles establish a well-mixed liquidwithin a shorter distance than spray coating devices that only employstatic mixers, thereby resulting in a shorter, lighter and lesscumbersome spray coating device 12.

FIG. 6 is a perspective view of the valve body 315 shown in FIG. 5. Aspreviously discussed, the valve body 315 includes the first baffle 340,the second baffle 342, and the downstream section 344. FIG. 6 alsoillustrates another perspective of the conduit 316 configured totransfer the second liquid from the annular cavity 314 to the centralopening 326, and the check valve shaft 320 configured to block the flowof first liquid into the central opening 326. As discussed in detailbelow, each baffle 340 and 342 includes at least one set of convergingpassages 402 configured to direct liquid flows toward one another in thedownstream direction 219. The present embodiment includes two sets oftwo converging passages 402. Alternative embodiments may include more orfewer sets of passages and/or more or fewer passages 402 per set. Forexample, certain embodiments may include 1, 2, 3, 4, 5, 6, 7, 8, or moresets of converging passages. Further embodiments may include 2, 3, 4, 5,6, 7, 8, or more passages 402 within each set. Because of the convergingarrangement, liquid exiting one passage of a set is directed towardliquid exiting another passage of the set. The impingement of the two ormore liquid streams establishes a turbulent flow that facilitatesadditional mixing of the first liquid with the second liquid.

The configuration of the second baffle 342 may be substantially similarto the configuration of the first baffle 340. However, in certainembodiments, the second baffle 342 is rotated about a longitudinal axisof the valve body 315, thereby establishing a circumferential offsetbetween the passages 402. In such embodiments, liquid exiting thepassages 402 of the first baffle 340 impinges upon an upstream surfaceof the second baffle 342, thereby establishing a turbulent flow thatfacilitates liquid mixing. In addition, the offset forces the liquid toflow in the circumferential direction 347 between the first baffle 340and the second baffle 342, thereby establishing a tortuous flow path. Aswill be appreciated, the more tortuous the flow path, the greater themixing effectiveness. For example, in certain configurations, a set ofpassages within the first baffle 340 may be rotated at leastapproximately 20, 45, 60, 80, 100, 120, 140, 160, 180, or more degreesrelative to a set of passages within the second baffle 342.

As illustrated, the valve body 315 also includes a pair of o-rings 404configured to establish a seal between the valve body 315 and the innersurface of the mixing portion 313. Specifically, the o-rings arepositioned on opposite longitudinal sides of the liquid conduits 316. Inthis configuration, the o-rings 404 serve to substantially maintain abarrier between the second liquid entering the conduits 316 and themixed liquid passing through the baffles 340 and 342. The valve body 315also includes a flange 406 configured to position the valve body 315within the mixing portion 313 of the body 202. Furthermore, asillustrated, each baffle 340 and 342 includes a flange 408 configured toestablish a gap between the baffles 340 and 342. This gap facilitatesmixing of the liquid exiting the first baffle 340 before flowing intothe second baffle 342. Consequently, the flanges 408 facilitate axialstacking (i.e., along an axial direction 343) of baffles within thevalve body 315. For example, while two baffles 340 and 342 are employedin the present embodiment, alternative embodiments may include more orfewer baffles, such as 1, 2, 3, 4, 5, 6, 7, 8, or more baffles.

FIG. 7 is a front view of the valve body 315, illustrating flow passages410 within the downstream portion 344. The flow passages 410 enable themixed liquid to flow from the baffles 340 and 342 to the downstreampassage 346. As illustrated, a gap between the flow passages 410facilitates placement of the conduits 316, such that the second liquidmay flow into the central opening 326 without contacting the downstreamflow of the mixed liquid. The present embodiment includes 10 circularpassages 410. Alternative embodiments may include passages 410 ofdifferent shapes, such as elliptical, square, or polygonal, for example.Further embodiments may include more or fewer passages. For example,certain embodiments may include more than 1, 2, 4, 6, 8, 10, 12, 14, 16,or more passages 410. Furthermore, a fastener 412 is coupled to thedownstream end of the valve body 315. The fastener 412 serves toseparate the flow of second liquid within the central opening 326 fromthe mixed liquid flowing through the passages 410.

FIG. 8 is a cross-sectional side view of the valve body 315, taken alongline 8-8 of FIG. 7. As illustrated, the flow passages 410 extend alongthe entire longitudinal extent of the downstream portion 344 of thevalve body 315. Therefore, the passages 410 serve to facilitate liquidflow from the baffles 340 and 342 to the downstream passage 346. Inaddition, FIG. 8 illustrates the spacing provided by the flanges 408.Specifically, the flange 408 of the second baffle 342 establishes anaxial gap 409 between the first baffle 340 and the second baffle 342 inthe axial direction 343. The axial gap 409 provides a space for liquidfrom the converging passages of the first baffle 340 to intersect andmix prior to flowing into the second baffle 342. Because each baffleincludes a flange 408, additional baffles may be axially stacked eitherupstream or downstream from the illustrated baffles 340 and 342, whileproviding an axial gap 409 between baffles for liquid mixing.

FIG. 9 is a perspective view of the mixing baffle 340. As previouslydiscussed, the baffle 340 includes two sets of flow passages, where eachset includes two passages 402. As illustrated, the sets of flow passagesare positioned approximately 180 degrees apart along the circumferenceof the baffle 340. The flow passages 402 within each set converge in thedownstream direction 219. Specifically, each flow passage includes aninlet 414 and an outlet 416. Because the inlets 414 are spaced fartherapart than the outlets 416, flows through the passages 402 are directedtoward one another. As the two flows intersect, a turbulent flow isestablished, thereby facilitating mixing of the liquids. As previouslydiscussed, the number of sets, the circumferential position of the setsand the number of passages 402 within each set may vary in alternativeembodiments.

In the present embodiment, the converging flow passages 402 areconfigured to direct liquid flows toward one another substantiallywithin a plane parallel to the axial direction 343. In alternativeembodiments, the converging flow passages 402 may be rotated in theradial direction 345 and/or the circumferential direction 347 such thatimpingement of one liquid upon another establishes a swirling liquidflow. This swirling flow may facilitate additional mixing of the firstand second liquids.

FIG. 10 is a cross-sectional bottom view of the mixing baffle 340, takenalong line 10-10 of FIG. 9. As illustrated, the flow passages 402converge toward an axial center line 418. Specifically, each passage 402forms an angle 420 with respect to the center line 418. In the presentembodiment, the angle 420 is approximately 45 degrees. Therefore, thepassages are oriented approximately 90 degrees relative to one another.In alternative embodiments, the angle 420 may be approximately between 5to 85, 10 to 80, 15 to 75, 20 to 70, 25 to 65, 30 to 60, 35 to 55, 40 to50, or about 45 degrees. By further example, the angle 420 may begreater than approximately 0, 10, 22.5, 30, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, or more degrees. As appreciated, larger angles 420 mayfacilitate enhanced mixing between the first and second liquids.However, a length 421 of the baffle 340 may be increased to accommodatethe larger angles 420, thereby increasing the length of the spraycoating device 12. Therefore, an angle 420 may be particularly selectedto both provide effective mixing of the liquids while limiting the spraycoating device length. In the present embodiment, liquid flows from thepassage outlets 416 flow in a direction 422 and impinge one another, asillustrated. As previously discussed, this impingement facilitatesenhanced mixing of the first and second liquids despite differences inflow rate and viscosity.

FIG. 11 is a perspective view of an alternative embodiment of the valvebody 315. Specifically, the alternative configuration is adapted formixing liquids that include abrasives. For example, certain resinsinclude a mineral filler such as calcium sulfate or alumina trihydratein concentrations ranging from approximately 10% to 50%. While thesemineral fillers provide enhanced qualities to certain FRP parts, theirabrasive nature causes significant wear to various internal componentsof the spray coating device 12. For example, the mixing baffles 340 and342 are particularly sensitive to such abrasive fillers. Therefore, analternative valve body 315 including a different baffle configurationmay be utilized when spraying resins that include mineral fillers.Furthermore, the valve body 315, and associated baffles, may beconstructed from a harder material, such as precipitation hardenedstainless steel, tungsten carbide, etc., to reduce wear.

As illustrated, the first baffle 340 is replaced with an alternativefirst baffle 502, and the second baffle 342 is replaced with analternative second baffle 504. The first baffle 502 includes a U-shapedrecess 506, and the second baffle 504 includes a U-shaped recess 508,positioned approximately 180 degrees from the recess 506 about thecircumference of the second baffle 504. As the liquid flow reaches thevalve body 315, the liquid is directed through the recess 506. Theliquid flow then impinges upon an upstream surface of the second baffle504, thereby establishing a turbulent flow that facilitates liquidmixing. The liquid is then forced to flow approximately 180 degrees inthe circumferential direction 347 to pass through the recess 508. Theposition of the recesses 506 and 508 establish a tortuous flow path thatserves to further mix the first liquid and the second liquid. Becausethe liquid is not directed through small converging passages, wear onthe baffles 502 and 504 may be reduced, thereby extending the usefullife of the valve body 315.

While the recess 508 is circumferentially offset approximately 180degrees in the present embodiment, alternative embodiments may havedifferent degrees of offset. For example, certain configurations mayinclude a circumferential offset greater than approximately 20, 40, 60,80, 100, 120, 140, 160, or more degrees. Further embodiments may includemultiple recesses within each baffle 502 and 504, such as 2, 3, 4, 5, 6,or more. Yet further embodiments may include additional baffles toprovide additional mixing of the liquids. This configuration may provideeffective mixing of the first and second liquids despite the absence ofconverging flow passages present in the previously described embodiment.

FIG. 12 is a cross-sectional front view of the spray coating device 12,taken along line 12-12 of FIG. 4, illustrating the liquid flushingsystem 228. As previously discussed, the liquid flushing system 228 isconfigured to flow a solvent through areas of the spray coating device12 where the first liquid is present. This process significantly reducesor eliminates the possibility that resin or other material may curewithin the spray coating device 12, thereby interfering with itsoperation. The liquid flushing system 228 includes an activation switch232, a shaft 602, and a compression spring 604. The liquid flushingsystem 228 is activated by depressing the switch 232, therebycompressing the spring 604 and driving the shaft 602 to move in adirection 606. Movement of the shaft 602 establishes a flow path fromthe solvent inlet 230 through an annular cavity 608 and an orifice 610in the liquid flushing system 228 to a first conduit 612. The solventthen flows through a second conduit 614 into the mixing chamber 328.From the mixing chamber 328, the solvent flows in the downstreamdirection 219 through each of the previously described elements andexits the spray tip 205. In this manner, each element that contacts thefirst liquid is exposed to the solvent such that the first liquid isflushed from the spray coating device 12. As previously discussed, thepresent embodiment facilitates effective mixing of liquids within ashorter distance than configurations which do not employ a counter flowarrangement and mixing baffles. Therefore, less solvent may be utilizedto flush the spray coating device 12, thereby reducing operationalcosts. Furthermore, because the mixing chamber 328 is positioneddirectly adjacent to the first liquid needle valve 329, flushing resinfrom additional areas within the body 202 is obviated.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

The invention claimed is:
 1. A system, comprising: a spray gun,comprising: a first liquid passage configured to flow a first liquid ina generally downstream direction toward a spray tip; a second liquidpassage configured to flow a second liquid in a generally upstreamdirection such that the second liquid impinges upon the first liquid atan outlet to the second liquid passage, wherein the upstream directionis substantially opposite from the downstream direction; a first mixingbaffle downstream from the outlet to the second liquid passage, andincluding a first recess configured to direct liquid flow toward animpingement surface; and a second mixing baffle downstream from thefirst mixing baffle, and including the impingement surface and a secondrecess; wherein the first recess of the first mixing baffle iscircumferentially offset from the second recess of the second mixingbaffle.
 2. The system of claim 1, comprising a check valve disposed atthe outlet to the second liquid passage and configured to block a flowof the first liquid into the second liquid passage, wherein the checkvalve forms a substantially annular orifice configured to provide agenerally even distribution of the second liquid into the first liquidpassage.
 3. The system of claim 1, wherein the first mixing baffle andthe second mixing baffle define a tortuous flow path.
 4. The system ofclaim 1, wherein the first recess and the second recess arecircumferentially offset approximately 180 degrees.
 5. The system ofclaim 1, wherein the first recess, the second recess, or a combinationthereof, is substantially U-shaped.
 6. The system of claim 1, comprisinga static mixer disposed downstream from the second mixing baffle, andincluding a plurality of turning vanes each configured to split androtate a liquid flow.
 7. The system of claim 1, wherein the spray tipcomprises an impingement tip including a plurality of converging exitorifices configured to direct streams of liquid toward one another. 8.The system of claim 1, wherein the spray gun comprises a liquid flushingsystem configured to provide solvent upstream of the outlet to thesecond liquid passage.
 9. A system, comprising: a spray gun, comprising:a first liquid passage configured to flow a first liquid in a generallydownstream direction toward a spray tip; a second liquid passageconfigured to flow a second liquid in a generally upstream directionsuch that the second liquid impinges upon the first liquid at an outletto the second liquid passage, wherein the upstream direction issubstantially opposite from the downstream direction; a check valvedisposed at the outlet to the second liquid passage and configured toblock a flow of the first liquid into the second liquid passage, whereinthe check valve forms a substantially annular orifice configured toprovide a generally even distribution of the second liquid into thefirst liquid passage; and at least one mixing baffle positioneddownstream from the outlet to the second liquid passage, wherein the atleast one mixing baffle is configured to mix the first liquid with thesecond liquid, and the at least one mixing baffle includes at least onerecess configured to direct a liquid flow toward an impingement surface.10. The system of claim 9, wherein the at least one mixing bafflecomprises a first mixing baffle and a second mixing baffle, the at leastone recess comprises a first recess in the first mixing baffle, and thesecond mixing baffle includes the impingement surface.
 11. The system ofclaim 10, wherein the at least one recess comprises a second recess inthe second mixing baffle, and the second recess of the second mixingbaffle is circumferentially offset from the first recess of the firstmixing baffle.
 12. The system of claim 11, wherein the first recess andthe second recess are circumferentially offset approximately 180degrees.
 13. The system of claim 9, wherein the at least one recess issubstantially U-shaped.
 14. The system of claim 9, wherein the at leastone mixing baffle defines a tortuous liquid flow path.
 15. A system,comprising: a multi-liquid mixing device, comprising: a first mixingbaffle including a first recess, wherein the first recess is configuredto direct a liquid flow toward an impingement surface; and a secondmixing baffle downstream from the first mixing baffle, and including theimpingement surface and a second recess; wherein the first recess of thefirst mixing baffle is circumferentially offset from the second recessof the second mixing baffle.
 16. The system of claim 15, wherein thesecond recess is configured to direct the liquid flow toward a secondimpingement surface.
 17. The system of claim 15, wherein the firstmixing baffle, the second mixing baffle, or a combination thereof, isformed from precipitation hardened stainless steel, tungsten carbide, ora combination thereof.
 18. The system of claim 15, wherein the firstrecess and the second recess are circumferentially offset approximately180 degrees.
 19. The system of claim 15, wherein the first recess, thesecond recess, or a combination thereof, is substantially U-shaped. 20.The system of claim 15, wherein the first mixing baffle and the secondmixing baffle define a tortuous liquid flow path.